Method for aligning one end of a passenger boarding bridge with a doorway of an aircraft

ABSTRACT

A method for aligning one end of a passenger boarding bridge with a doorway of an aircraft includes sensing a location of a base plate of the doorway of the aircraft, using a sensor that is disposed proximate the one end of the passenger boarding bridge. A current location of the one end of the passenger boarding bridge is then determined relative to the sensed location of the base plate. Based upon a known relationship between the location of the doorway and the sensed location of the base plate, the one end of the passenger boarding bridge is moved from the current location toward the doorway of the aircraft. The method relies upon features of the aircraft itself and does not require additional passive or active targets on the aircraft.

FIELD OF THE INVENTION

The instant invention relates to passenger boarding bridges, and moreparticularly to a method and system for aligning one end of a passengerboarding bridge with a doorway of an aircraft.

BACKGROUND

In order to make aircraft passengers comfortable, and in order totransport them between an airport terminal building and an aircraft insuch a way that they are protected from the weather and from otherenvironmental influences, passenger boarding bridges are used which aretelescopically extensible and the height of which is adjustable. Forinstance, an apron drive bridge includes a plurality of adjustablemodules, including: a rotunda, a telescopic tunnel, a bubble section, acab, and elevating columns with wheel carriage. Other common types ofpassenger boarding bridges include radial drive bridges andover-the-wing (OTW) bridges. These types of passenger boarding bridgesare adjustable, for instance to compensate for different sized aircraftand to compensate for imprecise parking of aircraft at an airportterminal.

Historically, the procedure for aligning the passenger boarding bridgewith the doorway of an aircraft has been a time consuming and laborintensive operation. First, the pilot taxis the aircraft along a lead-inline to a final parking position within a gate area. Typically, thelead-in line is a physical marker that is painted onto the tarmac, andis used for guiding the aircraft along a predetermined path to a finalparking position. Additional markings in the form of stop lines, one foreach type of aircraft, are provided at predetermined positions along thelead-in line. Thus, when the nose gear of a particular type of aircraftstops precisely at the stop line for that type of aircraft, then theaircraft is known to be at its final parking position. Of course, thepilot's view of the tarmac surface from the cockpit of an aircraft islimited. This is particularly true for larger aircraft, such as forinstance a Boeing 747-X00. Typically, in order to follow the lead-inline the pilot has relied upon instructions that are provided by a humanground marshal together with up to two “wing walkers”. Optionally, stopbars are located on a pole that is fixedly mounted to the groundsurface, including appropriate stop bars for each type of aircraft thatuses the gate. Alternatively, a tractor or tug is used to tow theaircraft along the lead-in line to its final parking position.

More recently, sophisticated Visual Docking Guidance Systems have beendeveloped to perform the function of the human ground marshal and wingwalkers. In particular, a Visual Docking Guidance System (VDGS) sensesthe aircraft as it approaches the final parking position and providesinstructions to the pilot via an electronic display device. Theelectronic display device is mounted at a location that makes it highlyvisible to the pilot when viewed from the cockpit of an aircraft.Typically, the instructions include a combination of alphanumericcharacters and symbols, which the pilot uses to guide the aircraftprecisely to the final parking position for the particular type ofaircraft. The high capital cost of the VDGS system is offset by reducedlabor costs and the efficiency that results from stopping the aircraftmore precisely than is possible under the guidance of a human groundmarshal.

Of course, even when the aircraft is stopped precisely at the finalparking position for that type of aircraft, still there is the matter ofmoving the passenger boarding bridge into an aligned relationship with adoorway of the parked aircraft. In the case of an apron drive bridgethis may involve extending the bridge by 10 to 20 meters or more from astowed position. Unfortunately, driving the bridge over such a longdistance is time consuming because often the rate at which the bridge ismoved is limited so as to reduce the risk of colliding with groundservice vehicles or personnel, and to avoid causing serious damage tothe aircraft in the event of a collision therewith. Manual,semi-automated and automated bridge alignment systems are known formoving the passenger boarding bridge relative to the parked aircraft.

A manual bridge alignment system requires that a human operator ispresent to perform the alignment operation each time an aircraftarrives. Delays occur when the human operator is not standing-by toperform the alignment operation as soon as the aircraft comes to a stop.In addition, human operators are prone to making errors that result inthe passenger boarding bridge being driven into the aircraft or into apiece of ground service equipment. Such collisions involving thepassenger boarding bridge are costly and also result in delays. In orderto avoid causing a collision, human operators tend to err on the side ofcaution and drive the passenger boarding bridge slowly and cautiously.

Semi-automated bridge alignment systems also require a human operator,but the human operator may be present at a remote location and interactwith the bridge control system in a tele-robotic manner. One humanoperator may interact with a plurality of different passenger boardingbridges, thereby reducing the costs associated with training and payingthe salaries of human operators. Alternatively, certain movements of thebridge are automated, whilst other movements are performed under thecontrol of the human operator.

Automated bridge alignment systems provide a number of advantagescompared to manual and semi-automated systems. For instance, automatedbridge alignment systems do not require a human operator, and thereforethe costs that are associated with training and paying the salaries ofhuman operators are reduced or eliminated. Furthermore, an automatedbridge alignment system is always standing by to control the passengerboarding bridge as soon as an aircraft comes to a stop. Accordingly,delays associated with dispatching a human operator to perform a bridgealignment operation are eliminated, particularly during periods of heavyaircraft traffic.

In U.S. Pat. No. 5,226,204, Schoenberger et al. disclose one type ofautomated system for aligning a passenger boarding bridge with a doorwayof an aircraft. The system uses video cameras to capture images of theaircraft. The captured images are then provided to a computer for imageprocessing. An object of the image processing is to use edge detectionto locate the outline of the doorway along the lateral surface of theaircraft, and to determine the distance and direction from the bridge tothe doorway. Unfortunately, the outline of the doorway does not providea high contrast feature, and accordingly it may be difficult to locatethe doorway within the image. In addition, the presence of scuffs, dirt,painted decals etc. near the doorway may make it difficult or impossibleto correctly identify the outline of the doorway.

Another type of automated system is disclosed in published United StatesPatent Application 2005/0198750 A1, filed Feb. 26, 2003 in the name ofSpencer et al. In particular, reflective targets are affixed to theexterior lateral surface of an aircraft around the doorway to which thepassenger boarding bridge is to be aligned. A plurality of camerasdisposed aboard the passenger boarding bridge is used to image thetargets during the alignment procedure, with data relating to the imagesbeing provided subsequently to computer means for processing thereby.While the use of reflective targets for identifying the doorway of theaircraft is advantageous in that it simplifies image processing,never-the-less airlines are reluctant to apply targets to their aircraftand furthermore regulatory approval may be necessary to do so. Inaddition, the system is likely to fail if the targets become obscureddue to dirt, scuffs, tearing or the build up of snow, etc. Furthermore,this approach relies upon every aircraft having the expected targetsapplied thereto. Absent the targets, it is not possible to align thepassenger boarding bridge in an automated fashion.

In another approach to automating the passenger boarding bridgealignment operation, a beacon signal is used to guide theaircraft-engaging end of a passenger boarding bridge into alignment withan aircraft doorway. In U.S. Pat. Nos. 7,093,314, 6,757,927, 6,742,210and 6,907,635, Hutton describes a transmitter or transceiver disposedaboard an aircraft for transmitting a signal including a beacon signal.A receiver aboard the passenger boarding bridge “homes in” on the beaconsignal until the aircraft-engaging end of the passenger boarding bridgeis aligned with the doorway of the aircraft. This approach relies uponevery aircraft being equipped with an appropriate transmitter ortransceiver. Absent the beacon signal, it is not possible to align thepassenger boarding bridge in an automated fashion.

There has been an apparent trend in recent years toward developingautomated passenger boarding bridge systems that rely upon additionalpassive or active targets, rather than features of the aircraft itself,for identifying the doorways of the aircraft. Accordingly, there is along-standing and unfulfilled need for a bridge alignment system that iscapable of aligning a passenger boarding bridge with an aircraft, absentintervention by a human operator, and absent additional passive oractive targets being mounted aboard the aircraft. It would beadvantageous to provide a system that overcomes at least some of theabove-mentioned disadvantages of the prior art.

SUMMARY OF EMBODIMENTS OF THE INVENTION

In accordance with an aspect of the instant invention there is provideda method for aligning one end of a passenger boarding bridge with adoorway of an aircraft, comprising: identifying the type and sub-type ofthe aircraft; positioning the one end of the passenger boarding bridgeat a predefined position for the identified type and sub-type of theaircraft; using an imager disposed proximate the one end of thepassenger boarding bridge, capturing image data relating to a portion ofa lateral surface of the aircraft, the doorway being defined within saidlateral surface; comparing the image data to template data for a doorwaybase plate of the identified type and sub-type of the aircraft;determining an instruction for moving the one end of the passengerboarding bridge toward the doorway of the aircraft, based on thecomparison of the image data with template data; and, automaticallyperforming the instruction so as to move the one end of the passengerboarding bridge toward the doorway of the aircraft.

In accordance with another aspect of the instant invention there isprovided a method for aligning one end of a passenger boarding bridgewith a doorway of an aircraft, comprising: identifying the type andsub-type of the aircraft; positioning the one end of the passengerboarding bridge at a predefined position for the identified type andsub-type of the aircraft; sensing a current orientation of the one endof the passenger boarding bridge; using an imager disposed proximate theone end of the passenger boarding bridge, capturing image data relatingto a portion of a lateral surface of the aircraft, the doorway beingdefined within said lateral surface; retrieving template data relatingto the base plate of the doorway of the identified type and sub-type ofthe aircraft; scaling the retrieved template data based on the sensedcurrent orientation of the one end of the passenger boarding bridge;determining an instruction for moving the one end of the passengerboarding bridge toward the doorway of the aircraft, based on acomparison of the captured image data to the scaled template data; and,automatically performing the instruction so as to move the one end ofthe passenger boarding bridge toward the doorway of the aircraft.

In accordance with another aspect of the instant invention there isprovided a method for aligning one end of a passenger boarding bridgewith a doorway of an aircraft, comprising: sensing a location of a baseplate of the doorway of the aircraft using a sensor that is disposedproximate the one end of the passenger boarding bridge; determining acurrent location of the one end of the passenger boarding bridgerelative to the sensed location of the base plate; and, moving the oneend of the passenger boarding bridge from the current location towardthe doorway of the aircraft, based upon a known relationship between thelocation of the doorway and the sensed location of the base plate.

A system for aligning one end of a passenger boarding bridge with adoorway of an aircraft, the aircraft being parked adjacent to the oneend of the passenger boarding bridge during a current alignmentoperation, the system comprising: an imager disposed proximate the oneend of the passenger boarding bridge for capturing image data relatingto a doorway base plate of the aircraft; a memory element havingtemplate image data stored therein, the template image data relating tothe doorway base plate of the aircraft; and a processor in communicationwith the imager and with the memory element, for comparing the capturedimage data with the template image data and for determining aninstruction for moving the one end of the passenger boarding bridgealong a direction toward the doorway of the aircraft, based on a resultof the comparison.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention will now be described inconjunction with the following drawings, in which similar referencenumbers designate similar items:

FIG. 1 is a simplified block diagram showing image capture elements andimage processing elements, according to an embodiment of the instantinvention;

FIG. 2 is a simplified flow diagram of a method for aligning one end ofa passenger boarding bridge with a doorway of an aircraft, according toan embodiment of the instant invention;

FIG. 3 is a simplified flow diagram of another method for aligning oneend of a passenger boarding bridge with a doorway of an aircraft,according to an embodiment of the instant invention; and,

FIG. 4 is a simplified flow diagram of still another method for aligningone end of a passenger boarding bridge with a doorway of an aircraft,according to an embodiment of the instant invention.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The following description is presented to enable a person skilled in theart to make and use the invention, and is provided in the context of aparticular application and its requirements. Various modifications tothe disclosed embodiments will be readily apparent to those skilled inthe art, and the general principles defined herein may be applied toother embodiments and applications without departing from the spirit andthe scope of the invention. Thus, the present invention is not intendedto be limited to the embodiments disclosed, but is to be accorded thewidest scope consistent with the principles and features disclosedherein.

According to at least one embodiment of the instant invention the baseplate of an aircraft doorway is recognized as a feature for locating thedoorway of the aircraft. To this end, an automated passenger boardingbridge control system is provided, which includes image capture elementsand image processing elements such as for instance at least a digitalcamera. FIG. 1 shows a non-limiting example of suitable image captureelements and image processing elements. Optionally, a more complexvision system is provided such as for instance the one that is describedby Hutton in a co-pending United States Patent Application entitled“Vision System For Automatically Aligning a Passenger Boarding Bridgewith a Doorway of an Aircraft and Method Therefor”, filed in October,2006, the entire contents of which are herein incorporated by reference.

It is to be understood that the doorway base plate is a feature of theaircraft itself, and is made of a hard metal so as to endure passengerfoot traffic during periods of boarding and deplaning. Typically, thebase plate either is not painted, or if it is painted then at least someof the paint is worn off due to passengers stepping on or rollingluggage across the base plate. Accordingly, the base plate tends to beshiny and contrasts with adjacent portions of the aircraft fuselage,particularly when illuminated using a light source. It has now beenrecognized that the base plate is a suitable feature for identifyinglocations of doorways of the aircraft, which overcomes the need toprovide passive or active targets for this purpose.

According to at least one embodiment of the instant invention, the typeand sub-type of the aircraft is determined and data relating to the typeand sub-type is provided to the automated passenger boarding bridgecontrol system. For instance, a human operator provides the type andsub-type information in a manual fashion. Optionally, the type andsub-type is determined based on a comparison of sensed features of theaircraft with template data. The automated passenger boarding bridgecontrol system then moves the passenger boarding bridge to a “photoposition” such that the aircraft-engaging end of the passenger boardingbridge is adjacent to an expected stopping location of the doorway ofthe determined type and sub-type of the aircraft. An image is capturedusing an imager that is disposed proximate the aircraft engaging end ofthe passenger boarding bridge, and image data relating to the image isprovided to an image data processor. Template data is retrieved from amemory element, the template data including at least one image of thedoorway of the determined type and sub-type of aircraft. Preferably thetemplate data includes a plurality of images of the doorway of thedetermined type and sub-type of aircraft. Optionally, at least some ofthe plurality of images includes paint pattern features of the doorwayand surrounding portions of the aircraft fuselage. The template data isscaled based on a sensed orientation of the passenger boarding bridgerelative to the aircraft. The captured image is compared to the scaledtemplate data so as to match features relating to the base plate in thecaptured image data and the scaled template data. Based upon thecomparison, horizontal and vertical movements of the passenger boardingbridge are determined for aligning the aircraft engaging end of thepassenger boarding bridge with the doorway of the aircraft. Once thehorizontal and vertical movements are performed, merely extending thelength of the passenger boarding bridge completes the alignmentoperation.

Referring to FIG. 1, shown is a simplified block diagram of image datacapture and image processing elements, according to an embodiment of theinstant invention. An imager 10, such as for instance a typical CCD orCMOS digital camera, is provided at a location proximate the one end ofthe passenger boarding bridge. The imager 10 is in communication with animage processor 12, and provides captured image data thereto forsubsequent processing, the captured image data relating to a doorwaybase plate of the aircraft. The image processor 12 is also incommunication with a memory element 14 having template image data storedtherein, the template image data relating to the doorway base plate ofthe aircraft. During use, the image processor 12 compares the capturedimage data with the template image data and, based on a result of thecomparison, determines an instruction for moving the one end of thepassenger boarding bridge along a direction toward the doorway of theaircraft. The image processor 12 provides an output signal including theinstruction for controlling a not illustrated drive mechanism of thepassenger boarding bridge. Based on the output signal, the notillustrated drive mechanism causes the one end of the passenger boardingbridge to move along the direction toward the doorway of the aircraft.

Optionally, a not illustrated light source is provided for illuminatingthe doorway base plate during image capture. Optionally, anorientation-sensing element such as for instance an inclinometer and/ora laser range finder is provided in communication with the imageprocessor 12. Optionally, the imager 10 is provided in the form of adigital camera that is capable of imaging near infrared (near IR) and/orultraviolet (UV), such as for instance a Fuji S3 UVIR. In this case,illumination using a light source may not be necessary or evendesirable. Optionally, the imager 10 comprises a plurality of digitalcameras. Of course, the imager 10 is not intended to be limited to onlyCCD or CMOS type digital cameras. Accordingly, it is envisaged that theimager 10 may utilize other types of image sensors that are capable ofconverting light into electrical signals.

Referring now to FIG. 2, shown is a simplified flow diagram of a methodfor aligning one end of a passenger boarding bridge with a doorway of anaircraft, according to an embodiment of the instant invention. At step100 the type and sub-type of the aircraft is identified. At step 102 theone end of the passenger boarding bridge is positioned at a predefinedposition for the identified type and sub-type of the aircraft. At step104 an imager disposed proximate the one end of the passenger boardingbridge is used for capturing image data relating to a portion of alateral surface of the aircraft, the doorway being defined within saidlateral surface. At step 106 the image data is compared to template datafor a doorway base plate of the identified type and sub-type of theaircraft. At step 108 an instruction is determined for moving the oneend of the passenger boarding bridge toward the doorway of the aircraft,based on the comparison of the image data with template data. At step110 the instruction is performed in an automated fashion so as to movethe one end of the passenger boarding bridge toward the doorway of theaircraft.

Referring now to FIG. 3, shown is a simplified flow diagram of anothermethod for aligning one end of a passenger boarding bridge with adoorway of an aircraft, according to an embodiment of the instantinvention. At step 200 the type and sub-type of the aircraft isidentified. At step 202 the one end of the passenger boarding bridge ispositioned at a predefined position for the identified type and sub-typeof the aircraft. At step 204 a current orientation of the one end of thepassenger boarding bridge is sensed relative to the aircraft. At step206 an imager disposed proximate the one end of the passenger boardingbridge is used for capturing image data relating to a portion of alateral surface of the aircraft, the doorway being defined within saidlateral surface. At step 208 template data relating to the base plate ofthe doorway of the identified type and sub-type of the aircraft isretrieved. At step 210 the retrieved template data is scaled based onthe sensed current orientation of the one end of the passenger boardingbridge relative to the aircraft. At step 212 an instruction isdetermined for moving the one end of the passenger boarding bridgetoward the doorway of the aircraft, based on a comparison of thecaptured image data to the scaled template data. At step 214 theinstruction is performed in an automated fashion so as to move the oneend of the passenger boarding bridge toward the doorway of the aircraft.

Referring now to FIG. 4, shown is a simplified flow diagram of stillanother method for aligning one end of a passenger boarding bridge witha doorway of an aircraft, according to an embodiment of the instantinvention. At step 300 a location of a base plate of the doorway of theaircraft is sensed using a sensor that is disposed proximate the one endof the passenger boarding bridge. At step 302 a current location of theone end of the passenger boarding bridge is determined relative to thesensed location of the base plate. At step 304 the one end of thepassenger boarding bridge is moved from the current location toward thedoorway of the aircraft, based upon a known relationship between thelocation of the doorway and the sensed location of the base plate.

Numerous other embodiments may be envisaged without departing from thespirit and scope of the invention.

What is claimed is:
 1. A method for aligning one end of a passengerboarding bridge with a doorway of an aircraft, comprising: identifyingthe type and sub-type of the aircraft; positioning the one end of thepassenger boarding bridge at a predefined position for the identifiedtype and sub-type of the aircraft; using an imager disposed proximatethe one end of the passenger boarding bridge, capturing image datarelating to a portion of a lateral surface of the aircraft, the doorwaybeing defined within said lateral surface; using an image processor incommunication with the imager, comparing the image data to template datafor a doorway base plate of the identified type and sub-type of theaircraft; determining an instruction for moving the one end of thepassenger boarding bridge toward the doorway of the aircraft, based onthe comparison of the image data with template data; and, automaticallyperforming the instruction so as to move the one end of the passengerboarding bridge toward the doorway of the aircraft.
 2. A methodaccording to claim 1, wherein the imager is a digital camera and whereincapturing image data comprises providing a signal relating to thecaptured image data from the digital camera to the image processor.
 3. Amethod according to claim 1, wherein the template data comprises aplurality of template images of the doorway base plate of the identifiedtype and sub-type of the aircraft.
 4. A method according to claim 3,wherein some of the plurality of template images include features of apaint pattern proximate the doorway of the aircraft.
 5. A methodaccording to claim 1, comprising sensing a current orientation of theone end of the passenger boarding bridge relative to the aircraft.
 6. Amethod according to claim 5, wherein comparing the image data totemplate data comprises scaling the template data based on the sensedcurrent orientation.
 7. A method according to claim 5, wherein sensingthe current orientation comprises sensing a distance from the imager tothe aircraft.
 8. A method according to claim 5, wherein sensing thecurrent orientation comprises sensing tilt of the one end relative to ahorizontal reference plane.
 9. A method for aligning one end of apassenger boarding bridge with a doorway of an aircraft, comprising:identifying the type and sub-type of the aircraft; positioning the oneend of the passenger boarding bridge at a predefined position for theidentified type and sub-type of the aircraft; sensing a currentorientation of the one end of the passenger boarding bridge; using animager disposed proximate the one end of the passenger boarding bridge,capturing image data relating to a portion of a lateral surface of theaircraft, the doorway being defined within said lateral surface; usingan image processor in communication with the imager, retrieving templatedata relating to the base plate of the doorway of the identified typeand sub-type of the aircraft; scaling the retrieved template data basedon the sensed current orientation of the one end of the passengerboarding bridge; determining an instruction for moving the one end ofthe passenger boarding bridge toward the doorway of the aircraft, basedon a comparison of the captured image data to the scaled template data;and, automatically performing the instruction so as to move the one endof the passenger boarding bridge toward the doorway of the aircraft. 10.A method according to claim 9, wherein the imager is a digital cameraand wherein capturing image data comprises providing a signal relatingto the captured image data from the digital camera to the imageprocessor.
 11. A method according to claim 9, wherein the template datacomprises a plurality of template images of the doorway base plate ofthe identified type and sub-type of the aircraft.
 12. A method accordingto claim 11, wherein some of the plurality of template images includefeatures of a paint pattern proximate the doorway of the aircraft.
 13. Amethod according to claim 9, wherein sensing the current orientationcomprises sensing a distance from the imager to the aircraft.
 14. Amethod according to claim 9, wherein sensing the current orientationcomprises sensing tilt of the one end relative to a horizontal referenceplane.
 15. A method for aligning one end of a passenger boarding bridgewith a doorway of an aircraft, comprising: sensing a location of a baseplate of the doorway of the aircraft using a sensor that is disposedproximate the one end of the passenger boarding bridge; determining acurrent location of the one end of the passenger boarding bridgerelative to the sensed location of the base plate; and, moving the oneend of the passenger boarding bridge from the current location towardthe doorway of the aircraft, based upon a known relationship between thelocation of the doorway and the sensed location of the base plate.
 16. Amethod according to claim 15, wherein the sensor comprises a digitalcamera and wherein sensing a location of the base plate comprisescapturing a digital image of the base plate of the doorway.
 17. A methodaccording to claim 16, wherein determining a current location of the oneend of the passenger boarding bridge relative to the sensed location ofthe base plate comprises comparing the captured digital image withstored template data.
 18. A method according to claim 17, wherein thestored template data comprises a plurality of template images of thedoorway base plate.
 19. A method according to claim 18, wherein some ofthe plurality of template images include features of a paint patternproximate the doorway of the aircraft.
 20. A method according to claim17, comprising scaling the stored template data based on a sensedorientation of the one end relative to the aircraft.
 21. A system foraligning one end of a passenger boarding bridge with a doorway of anaircraft, the aircraft being parked adjacent to the one end of thepassenger boarding bridge during a current alignment operation, thesystem comprising: an imager disposed proximate the one end of thepassenger boarding bridge for capturing image data relating to a doorwaybase plate of the aircraft; a memory element having template image datastored therein, the template image data relating to the doorway baseplate of the aircraft; and a processor in communication with the imagerand with the memory element, for comparing the captured image data withthe template image data and for determining an instruction for movingthe one end of the passenger boarding bridge along a direction towardthe doorway of the aircraft, based on a result of the comparison.
 22. Asystem according to claim 21, wherein the imager is a digital camera.23. A system according to claim 22, comprising a light source forilluminating the doorway base plate of the aircraft during image captureby the digital camera.
 24. A system according to claim 21, comprising anorientation sensing element for sensing an orientation of the one end ofthe passenger boarding bridge.
 25. A system according to claim 24,wherein the orientation sensing element is an inclinometer incommunication with the processor for sensing an orientation of the oneend of the passenger boarding bridge relative to a horizontal referenceplane.
 26. A system according to claim 24, wherein the orientationsensing element is a laser range finder for sensing a distance from theimager to the aircraft.